The app currently requires you to take 2 tests every other day. The first test that you do grants you with 2 energy points, the second (if done the same day) grants you with 3. If you complete both tests on the same day, you will receive 5 energy points. On the next day, which will be a rest day, you will automatically receive 5 energy points without having to do a test.
The energy points are not cumulative. Each night, the count is reset to zero. It is impossible to keep energy points for another day. Do your vision test of the day to get energy points and to be able to play the puzzles.